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Re: [Healeys] Laycock overdrive

To: Hank Leach <gradea1@charter.net>
Subject: Re: [Healeys] Laycock overdrive
From: Bob Spidell via Healeys <healeys@autox.team.net>
Date: Sat, 12 Aug 2023 12:18:02 -0700
Cc: "'healeys@autox.team.net'" <healeys@autox.team.net>
Delivered-to: mharc@autox.team.net
Delivered-to: healeys@autox.team.net
References: <c02183110a608b1b7fa676318c90572c41f2fd02@webmail>
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I think the fact Laycock went from steel rings on the operating pistons 
to O-rings is telling. Both will wear, but the steel rings will score 
the cylinder.


On 8/12/2023 9:40 AM, Hank Leach wrote:
> Bob-good point.  I just got a set of springs from Moss (from OD Spares 
> in UK, I imagine). The cost was $99 or about $12/spring which in the 
> scope of things is really not relevant. Holding that clutch in tight 
> contact to the brake ring is paramount and just imagine the number of 
> miles in direct drive that the car has experienced...many at high RPM. 
> The other side of the brake for overdrive position is the "lazy side" 
> as the operating pistons under hydraulic pressure have plenty of clout 
> driving mostly steady RPMs. Yes, springs wear out.
>
> I place them on the bench and line up the lengths. They should measure 
> 4-1/2" for the long springs and 4-1/4" for the short ones but 
> invariably there is differences in the resting length. After 50+ years 
> of pushing you would tend to get tired. When in overdrive, the springs 
> are greatly depressed.  That is asking a lot for spiral metal to 
> accomplish. So, yes they may look good, but have poor stamina-oops, I 
> just describe all of us. Hank
>
> -----------------------------------------
>
> From: "Bob Spidell"
> To: healeys@autox.team.net
> Cc:
> Sent: Friday August 11 2023 9:19:34PM
> Subject: Re: [Healeys] Laycock overdrive
>
> re: "... The health of the 8 springs that keep the unit in direct drive
> is important to keep the clutch from slipping...."
>
> I believe the shop manual admonishes owners to replace these when
> overhauling the unit, even if the old ones look and feel fine (some say
> not so). I think my old ones are in a box on a shelf somewhere if
> anybody wants them.
>
> Note the O/D pump is a positive displacement pump that will continue to
> produce pressure--driven by the full power of the engine--unless there
> is a pressure relief mechanism.
>
>
> On 8/11/2023 10:34 AM, Hank Leach via Healeys wrote:
> > Guys-this is a very lively topic and one of sometimes great mystery
> > and confusion.  The unit is complex but the end result is working well
> > or not functioning at all.
> >
> > On the subject of pressure required to operate the shift into
> > overdrive there are many schools of thought. Some people replace or
> > stretch springs or add washers to increase the pressure needed. The
> > health of the 8 springs that keep the unit in direct drive is
> > important to keep the clutch from slipping.  The pressure supplied to
> > overcome the strength of these 8 spring , and effect overdrive, relies
> > on adequate hydraulic pressure. The change from direct to overdrive
> > needs to be smooth, not harsh, and if pressures are high the unit will
> > snap into and out of OD rather than the smooth interchange we are used
> > to while driving.
> >
> > When applied to the Austin Healey 100, the Laycock overdrive was
> > initially a 32% reduction unit. It was soon found out in these early
> > Warwick cars that 32% was too much reduction.  DHMC swapped units
> > three times in the original DMH tour car until they finally found a
> > combination that produced the smooth shift and complimentary gearing
> > desired.
> >
> > It is difficult, today, to find any information on this original 32%
> > gearbox, however if you examine the booklet (attached) supplied by
> > Laycock for the early cars, you will notice that the casting allowed
> > for a large accumulator piston (seen on p6 in brochure). After some
> > research and modified engineering, the company came up with this alloy
> > "sleeve" called the piston housing (photo) which partially filled the
> > chamber of the original large accumulator casting and allowed for a
> > smaller accumulator piston that we see in all the later 28% reduction
> > units. That size piston, in proper condition, produced from 350-450
> > lbs of needed hydraulic pressure to overcome the springs influence.
> >
> > I'm confident that the remark made by Geoff Healey in his writings
> > about the early transmissions "harsh shifting" revolved around this
> > huge accumulator piston producing too much pressure. Additionally,
> > there were three various accumulator springs supplied which adjusted
> > the pressure. The early boxes produced about 350lbs and the later
> > about 450.
> >
> > Today, Overdrive Spares supplies that sleeve housing with only one
> > rubber O-ring as it is basically a filler part and not under extreme
> > pressure. The accumulator piston within is under that pressure. They
> > supply a modified piston using O-ring technology. So, it is not
> > unusual to get good pressures over the normal 450 lbs required. If it
> > works well don't fix it.  The only concern is if the pressure does not
> > release when overdrive is not called for. A clean unit, with proper
> > 30W oil, will allow that to happen. All this some old theory and
> > history to ponder. Hank

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    I think the fact Laycock went from steel rings on the operating
    pistons to O-rings is telling. Both will wear, but the steel rings
    will score the cylinder.<br>
    <br>
    <br>
    <div class="moz-cite-prefix">On 8/12/2023 9:40 AM, Hank Leach wrote:<br>
    </div>
    <blockquote type="cite"
      cite="mid:c02183110a608b1b7fa676318c90572c41f2fd02@webmail">
      <meta http-equiv="content-type" content="text/html; charset=UTF-8">
      Bob-good point.  I just got a set of springs from Moss (from OD
      Spares in UK, I imagine). The cost was $99 or about $12/spring
      which in the scope of things is really not relevant. Holding that
      clutch in tight contact to the brake ring is paramount and just
      imagine the number of miles in direct drive that the car has
      experienced...many at high RPM. The other side of the brake for
      overdrive position is the "lazy side" as the operating pistons
      under hydraulic pressure have plenty of clout driving mostly
      steady RPMs. Yes, springs wear out.
      <div><br>
      </div>
      <div>I place them on the bench and line up the lengths. They
        should measure 4-1/2" for the long springs and 4-1/4" for the
        short ones but invariably there is differences in the resting
        length. After 50+ years of pushing you would tend to get tired.
        When in overdrive, the springs are greatly depressed.  That is
        asking a lot for spiral metal to accomplish. So, yes they may
        look good, but have poor stamina-oops, I just describe all of
        us. Hank<br>
        <br>
        <p>-----------------------------------------</p>
        From: "Bob Spidell" <bspidell@comcast.net><br>
          To: <a class="moz-txt-link-abbreviated" 
href="mailto:healeys@autox.team.net";>healeys@autox.team.net</a><br>
          Cc: <br>
          Sent: Friday August 11 2023 9:19:34PM<br>
          Subject: Re: [Healeys] Laycock overdrive<br>
          <br>
          re: "... The health of the 8 springs that keep the unit in
          direct
          drive<br>
          is important to keep the clutch from slipping...."<br>
          <br>
          I believe the shop manual admonishes owners to replace these
          when<br>
          overhauling the unit, even if the old ones look and feel fine
          (some
          say<br>
          not so). I think my old ones are in a box on a shelf somewhere
          if<br>
          anybody wants them.<br>
          <br>
          Note the O/D pump is a positive displacement pump that will
          continue to<br>
          produce pressure--driven by the full power of the
          engine--unless
          there<br>
          is a pressure relief mechanism.<br>
          <br>
          <br>
          On 8/11/2023 10:34 AM, Hank Leach via Healeys wrote:<br>
          &gt; Guys-this is a very lively topic and one of sometimes
          great
          mystery<br>
          &gt; and confusion.  The unit is complex but the end result is
          working well<br>
          &gt; or not functioning at all.<br>
          &gt;<br>
          &gt; On the subject of pressure required to operate the shift
          into<br>
          &gt; overdrive there are many schools of thought. Some people
          replace or<br>
          &gt; stretch springs or add washers to increase the pressure
          needed. The<br>
          &gt; health of the 8 springs that keep the unit in direct
          drive
          is<br>
          &gt; important to keep the clutch from slipping.  The pressure
          supplied to<br>
          &gt; overcome the strength of these 8 spring , and effect
          overdrive, relies<br>
          &gt; on adequate hydraulic pressure. The change from direct to
          overdrive<br>
          &gt; needs to be smooth, not harsh, and if pressures are high
          the
          unit will<br>
          &gt; snap into and out of OD rather than the smooth
          interchange we
          are used<br>
          &gt; to while driving.<br>
          &gt;<br>
          &gt; When applied to the Austin Healey 100, the Laycock
          overdrive
          was<br>
          &gt; initially a 32% reduction unit. It was soon found out in
          these
          early<br>
          &gt; Warwick cars that 32% was too much reduction.  DHMC
          swapped units<br>
          &gt; three times in the original DMH tour car until they
          finally
          found a<br>
          &gt; combination that produced the smooth shift and
          complimentary
          gearing<br>
          &gt; desired.<br>
          &gt;<br>
          &gt; It is difficult, today, to find any information on this
          original 32%<br>
          &gt; gearbox, however if you examine the booklet (attached)
          supplied by<br>
          &gt; Laycock for the early cars, you will notice that the
          casting
          allowed<br>
          &gt; for a large accumulator piston (seen on p6 in brochure).
          After
          some<br>
          &gt; research and modified engineering, the company came up
          with
          this alloy<br>
          &gt; "sleeve" called the piston housing (photo) which
          partially
          filled the<br>
          &gt; chamber of the original large accumulator casting and
          allowed
          for a<br>
          &gt; smaller accumulator piston that we see in all the later
          28%
          reduction<br>
          &gt; units. That size piston, in proper condition, produced
          from
          350-450<br>
          &gt; lbs of needed hydraulic pressure to overcome the springs
          influence.<br>
          &gt;<br>
          &gt; I'm confident that the remark made by Geoff Healey in his
          writings<br>
          &gt; about the early transmissions "harsh shifting" revolved
          around
          this<br>
          &gt; huge accumulator piston producing too much pressure.
          Additionally,<br>
          &gt; there were three various accumulator springs supplied
          which
          adjusted<br>
          &gt; the pressure. The early boxes produced about 350lbs and
          the
          later<br>
          &gt; about 450.<br>
          &gt;<br>
          &gt; Today, Overdrive Spares supplies that sleeve housing with
          only
          one<br>
          &gt; rubber O-ring as it is basically a filler part and not
          under
          extreme<br>
          &gt; pressure. The accumulator piston within is under that
          pressure. They<br>
          &gt; supply a modified piston using O-ring technology. So, it
          is
          not<br>
          &gt; unusual to get good pressures over the normal 450 lbs
          required. If it<br>
          &gt; works well don't fix it.  The only concern is if the
          pressure does not<br>
          &gt; release when overdrive is not called for. A clean unit,
          with
          proper<br>
          &gt; 30W oil, will allow that to happen. All this some old
          theory
          and<br>
          &gt; history to ponder. Hank</bspidell@comcast.net><br>
      </div>
    </blockquote>
    <br>
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